1. Field of the Invention
The present invention relates in general to internal combustion engines having a variable compression ratio mechanism by which the compression ratio of the engine can be varied, and more particularly to internal combustion engines having the variable compression ratio mechanism of a double-link type.
2. Description of the Prior Art
In order to clarify the task of the present invention, one known internal combustion engine of the above-mentioned type will be briefly described with reference to FIG. 42 of the accompanying drawings, which is shown in a paper xe2x80x9cMTZ Motortechnische Zeitschrift 58xe2x80x9d issued in 1997 in Germany.
As shown in the drawing, the engine having a variable compression ratio mechanism incorporated therewith is of a four cylinder type.
The mechanism comprises four upper links 2 each having one end pivotally connected to a piston pin 1a of a corresponding piston 1, four lower links 4 each being pivotally disposed on a crank pin of a crankshaft 3 and having one end pivotally connected to the corresponding upper link 2, a control shaft 5 extending in parallel with the crankshaft 3 and four control links 6 each having one end pivotally connected to the corresponding upper link 2 and the other end pivotally connected to the control shaft 5 through an eccentric cam 5a. When the control shaft 5 is rotated about its axis to an angular position, the fulcrum of each control link 6 is changed and thus the actual distance between the piston pin 1a and the corresponding crank pin of the crankshaft 3 is varied changing the stroke of the piston 1. Due to change of the piston stroke, the compression ratio of the engine can be varied.
However, due to its inherent construction, the variable compression ratio mechanism of the above-mentioned type has failed to provide the engine with a compact construction. That is, provision of the control shaft 5, which is positioned away from the crankshaft 3 in a lateral direction of the engine, causes a largely expanded structure of one side wall of a cylinder block of the engine.
It is therefore an object of the present invention to provide an internal combustion engine with a compact variable compression ratio mechanism.
It is another object of the present invention to provide a variable compression ratio mechanism which can be compactly installed in an internal combustion engine.
According to the present invention, there is provided an internal combustion engine which comprises a cylinder block having a cylinder in which a piston reciprocates; a crankshaft rotatably installed in the cylinder block and including a crank pin and a counter-weight; and a variable compression ratio mechanism including an upper link having one end pivotally connected to a piston pin of the piston, a lower link pivotally disposed on the crank pin of the crankshaft and having one part pivotally connected to the other end of the upper link, a control shaft extending substantially in parallel with the crankshaft, a control link having a first end pivotally connected to the other part of the lower link and an eccentric bearing structure through which a second end of the control link is connected to the control shaft, so that rotation of the control shaft about its axis induces a pivoting of the lower link about said crank pin thereby to vary the stroke of the piston.